Beat together the butter, 1 tablespoon orange zest, salt and 180g sugar until light and fluffy.
Add the flour and knead into a smooth dough. Wrap in plastic wrap and chill for two hours in the fridge. Preheat oven to 200 degrees C.
Roll out the dough to 1cm thick on a floured work surface. Cut out cookies with star shaped cutters and place on a lined baking tray. Bake 13-15 minutes until golden brown.
In a bowl crush together the vanilla sugar with the 1 teaspoon zest until mixed well. Dip the cookies in the sugar while still warm.